Add DeepTest agentic workflow for automated test generation (#8432)

* Initial plan

* Create DeepTest agentic workflow for test generation

Co-authored-by: saikat107 <2145576+saikat107@users.noreply.github.com>

* Add documentation for DeepTest workflow

Co-authored-by: saikat107 <2145576+saikat107@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: saikat107 <2145576+saikat107@users.noreply.github.com>

.github/workflows/deeptest.md

@@ -0,0 +1,66 @@
+---
+description: Generate comprehensive test cases for Z3 source files
+
+on:
+  workflow_dispatch:
+    inputs:
+      file_path:
+        description: 'Path to the source file to generate tests for (e.g., src/util/vector.h)'
+        required: true
+        type: string
+      issue_number:
+        description: 'Issue number to link the generated tests to (optional)'
+        required: false
+        type: string
+  slash_command:
+    name: deeptest
+    events: [issues, issue_comment, pull_request, pull_request_comment]
+
+permissions: read-all
+
+network: defaults
+
+tools:
+  cache-memory: true
+  serena: ["python"]
+  github:
+    toolsets: [default]
+  bash: [":*"]
+  edit: {}
+  glob: {}
+  grep: {}
+
+safe-outputs:
+  create-pull-request:
+    title-prefix: "[DeepTest] "
+    labels: [automated-tests, deeptest]
+    draft: false
+  add-comment:
+    max: 2
+  missing-tool:
+    create-issue: true
+
+timeout-minutes: 30
+
+steps:
+  - name: Checkout repository
+    uses: actions/checkout@v5
+
+---
+
+<!-- Edit the file linked below to modify the agent without recompilation. Feel free to move the entire markdown body to that file. -->
+{{#runtime-import agentics/deeptest.md}}
+
+## Context
+
+You are the DeepTest agent for the Z3 theorem prover repository.
+
+**Workflow dispatch file path**: ${{ github.event.inputs.file_path }}
+
+**Issue number** (if linked): ${{ github.event.inputs.issue_number }}
+
+If triggered by a slash command (`/deeptest`), extract the file path from the issue or comment text.
+
+## Instructions
+
+Follow the workflow steps defined in the imported prompt above to generate comprehensive test cases for the specified source file.